This document discusses methods of estimating evaporation and runoff. It describes different types of pans that can be used to directly measure evaporation, as well as theoretical methods like the water, energy and mass budget approaches. It also discusses factors that influence infiltration and various formulas that can be used to compute runoff, including the rational method. Hydrographs and unit hydrographs are introduced to analyze streamflow over time from rainfall-runoff events.

1. NUST Institute of Civil Engineering/Engr Sajjad Ahmad1

2. Engineering Hydrology(CE- 235)CHAPTER - 32Runoff & Hydrographs(Contd…)NUST Institute of Civil Engineering/Engr Sajjad AhmadRunoff & hydrograph - OutlineEstimation of evaporation

3. Direct measurement

4. Indirect or theoretical method

5. Measurement of infiltration3Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad AhmadRunoff & hydrograph - OutlineComputation of runoff by various methods

6. Characteristics of hydrograph

7. Components of a hydrograph

8. Hydrograph separation

9. Unit Hydrograph

10. S-curve4Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad Ahmad5Engineering Hydrology(CE- 235)Direct measurement of evaporation by Pan There are three types of panSunken pans

11. Above ground or surface pans

12. Floating pans

13. NUST Institute of Civil Engineering/Engr Sajjad Ahmad6Engineering Hydrology(CE- 235)Sunken pansBuried in ground

14. Wall effects such as heat exchange and ration effects are neglected

15. More accurate results

16. NUST Institute of Civil Engineering/Engr Sajjad Ahmad7Engineering Hydrology(CE- 235)Sunken pans drawbacksDifficult to clean

17. Error due to leakage

18. Height of vegetation around pan is critical

19. Plant leaves, seeds and debris can enter easily

20. NUST Institute of Civil Engineering/Engr Sajjad Ahmad8Engineering Hydrology(CE- 235)Bureau of plant industry (B. P. I) panCircular in shape

21. 1.80 m in diameter and 0.55m deep

22. Edges are 0.05m above ground

23. Total depth is 0.60m

24. NUST Institute of Civil Engineering/Engr Sajjad Ahmad9Engineering Hydrology(CE- 235)Colorado panSquare in shape

25. Dimensions are 0.90m x 0.90m and 0.45m deep

26. Rim projection from ground is 5 cm

27. Water maintained 2 inch below rim

28. NUST Institute of Civil Engineering/Engr Sajjad Ahmad10Engineering Hydrology(CE- 235)Young’s panCircular shape

29. 0.6m diameter

30. 0.9m deep

31. Covered with 6mm wire mesh screen

32. NUST Institute of Civil Engineering/Engr Sajjad Ahmad11Engineering Hydrology(CE- 235)Above ground or surface panMade from galvanized sheet

33. Placed on wooden floor

34. Easy operation and maintenance

35. Correction factors are applied

36. NUST Institute of Civil Engineering/Engr Sajjad Ahmad12Engineering Hydrology(CE- 235)Floating pansFloat over surface of water

37. Gives accurate reading which are free from atmospheric effects

38. Drawbacks

39. Difficulty in measurement

40. Leakage cannot be detected

41. NUST Institute of Civil Engineering/Engr Sajjad Ahmad13Engineering Hydrology(CE- 235)Estimation by theoretical methodWater budget approach

42. Energy budget approach

43. Mass transfer approach

44. NUST Institute of Civil Engineering/Engr Sajjad Ahmad14Engineering Hydrology(CE- 235)Water budget approachNUST Institute of Civil Engineering/Engr Sajjad Ahmad15Engineering Hydrology(CE- 235)Energy budget approachNUST Institute of Civil Engineering/Engr Sajjad Ahmad16Engineering Hydrology(CE- 235)Energy budget approachNUST Institute of Civil Engineering/Engr Sajjad Ahmad17Engineering Hydrology(CE- 235)Mass transfer approachNUST Institute of Civil Engineering/Engr Sajjad Ahmad18Engineering Hydrology(CE- 235)Mass transfer approachNUST Institute of Civil Engineering/Engr Sajjad Ahmad19Engineering Hydrology(CE- 235)Pan coefficientMeasured evaporation is always greater than the actual value

45. The coefficient multiplier of 0.6 or greater is used to get actual reading

46. This coefficient is termed as pan coefficient

47. NUST Institute of Civil Engineering/Engr Sajjad Ahmad20Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad Ahmad21Engineering Hydrology(CE- 235)Example # 1 (from book)Example # 2 (from book)Example # 3 (from book)Example # 4 (from book)Example # 5(from book)NUST Institute of Civil Engineering/Engr Sajjad AhmadLysimeterA lysimeter is a measuring device which can be used to measure the amount of actual evapotranspiration which is released by crops or trees. By recording the amount of precipitation that an area receives and the amount lost through the soil, the amount of water lost to evapotranspiration can be calculated22Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad Ahmad23Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad AhmadInfiltrationWater loss due to absorption of water by the ground surface

48. Horizontal movement of absorbed water is called interflow